module RequiresParameters #:nodoc:
  def requires!(hash, *params)
    params.each do |param| 
      if param.is_a?(Array)
        raise ArgumentError.new("Missing required parameter: #{param.first}") unless hash.has_key?(param.first) 

        valid_options = param[1..-1]
        raise ArgumentError.new("Parameter: #{param.first} must be one of #{valid_options.to_sentence(:connector => 'or')}") unless valid_options.include?(hash[param.first])
      else
        raise ArgumentError.new("Missing required parameter: #{param}") unless hash.has_key?(param) 
      end
    end
  end    
end